The FDA action comes five years after patients complained of headaches and returning depression after switching from brand-name Wellbutrin XL to Teva's generic version. The Teva generic was approved in December 2006.

In 2009, the FDA wrongly assured patients that the Teva generic worked just as well as the name brand. But it wasn't until 2010 that the FDA finally decided to test the full-dose version of the drug. Those tests, completed just weeks ago, found that instead of proper extended release, Teva's drug dumped too much active ingredient too soon and failed to maintain effective drug levels.

The FDA tests in people finally came to the same conclusion as October 2007 lab tests by Tod Cooperman, MD. Cooperman's for-profit company, the ConsumerLab web site, tests nutritional supplements and generic drugs for potency and accurate labeling.

"The generic did not act like a once-a-day formula but more like an immediate-release formula," Cooperman says.

Teva and Impax Laboratories, which makes the drug for Teva, have recalled the drug. The lower-dose version, Budeprion XL 150 mg, remains on the market. FDA's waived tests of the now-withdrawn 300-mg version of the drug based on tests of the lower-dose version -- a process called "waiving up."

The FDA defended the practice, noting that generic drugs are tested on small numbers of healthy volunteers to see if they work the same as (are "bioequivalent" to) brand-name drugs. The agency was reluctant to expose these volunteers to the side effects of the higher-dose drug.

"A less cautious approach in studying the bioequivalencies of Budeprion XL 300 mg could have brought the data to light earlier," the FDA admits on its web site.

Alternative Generic Wellbutrin Products

However, the FDA has asked each of these manufacturers to test the drugs at full dose to see if they truly are the same as the brand-name antidepressant.

It's likely they are. Most of the complaints received by the FDA concerned the Teva/Impax drug.

Are Generic Drugs Safe and Effective?

Withdrawal of the Teva generic shows that the FDA's system for ensuring the safety and effectiveness of generic drugs works, says the Generic Pharmaceutical Association (GPhA), the trade group representing generic drugmakers.

"The recall by a single manufacturer of one strength of a generic drug should in no way cast doubt on the impeccable reputation of the generic industry or the FDA in our joint commitment to patient safety," says Ralph G. Neas, president and CEO of the GPhA.

According to the group, there are more than 10,000 FDA-approved generic drugs in the U.S. Of the 4 billion prescriptions filled in the U.S. each year, almost 80% are for generic drugs.

A major reason generic drugs cost less than brand-name drugs is that generic drugmakers don't have to perform extensive safety and effectiveness testing. They only have to show, usually in a small number of healthy volunteers, that their drugs deliver the same active ingredients in the same way as brand-name drugs.

The FDA says generic drugs are just as good as brand-name drugs. As an example, it points to a study that analyzed 38 clinical trials comparing generic to name-brand heart drugs. The study found that the generics performed just as well.

However, the Teva withdrawal -- and the FDA's request for more tests of other Wellbutrin generics -- suggests that at least for extended-release drugs, the FDA's testing process may have been flawed.

The FDA says it's looking into this and other issues. In a recently revised generic drugs fact sheet on its web site, the agency notes:

"FDA is aware that there are reports noting that some people may experience an undesired effect when switching from brand name drug to a generic formulation or from one generic drug to another generic drug. FDA wants to understand what may cause problems with certain formulations if, in fact, they are linked to specific generic products.

"FDA is encouraging the generic industry to investigate whether, and under what circumstances, such problems occur. The Agency does not have the resources to perform independent clinical studies and lacks the regulatory authority to require industry to conduct such studies. FDA will continue to investigate these reports to ensure that it has all the facts about these treatment failures and will make recommendations to healthcare professionals and the public if the need arises."